nested heirarchies as evidence against darwinian evolution

The thread topic is not to debate to what degree phyla were appearing prior to the Cambrian explosion, which is a subject of some debate, nor to be exact over that time period, which is why I rounded to 500 million years instead of 520 million years. The point is that in hundreds of millions of years, roughly 500 million years, no new animal phyla have evolved.Apparently whatever process or mechanism was involved in originating the animal phyla stopped roughly 500 million years ago, most earler and maybe one 470 million years, but why quibble here......500 million is a good approximation based on evo dating.Why have no new animal phyla evolved since then?

Arbitrary? I hope not. My understanding is that the groupings were based on factual analysis. Is that incorrect in your opinion?As to the rest of your post, I already answered you earlier and you have not responded. There are still, for example, non-vertebrates around. There is no valid reason why new strains of vertebrates would not evolve as well as all sorts of new phyla.Edited by randman, : No reason given.

Yes, the groupings are based on analysis. The names of the groupings is manmade and arbitrary. "If we evolved from apes, why are there still apes around?", you've just moved the old silly argument back a few orders of magnitude. Why not push it back further:- why are there still non-animals around?

You are ignoring that if only 8 phyla are known from the 'Cambrian explosion' then then rest of the 33 must have originated after. Bryozoa are one that comes to mind, they are critical reef animals in the Ordovician that did not exist until after the Cambrian.

How is this a silly argument? To point out that we have the same sorts of organisms that suppossed originally evolved into all the phyla but they stopped doing so 500 million years ago.It looks like you are just dodging the argument, modulous.

All but one phyla existed at the time of the Cambrian explosion, not just 8, and the one may have as well, but we only have fossils from 470 million years ago based on evo dating.If you really disagree, provide a link and some evidence, please.Note: Bryozoa - WikipediaThey are the one possible exception that could have appeared 470 million years ago, but even there, it's just as likely they appeared earlier during the Cambrian explosion and not later.That still doesn't change the facts, nor my point. Basically, we haven't seen any new animal phyla in rougly 500 million years with the possibility of one 470 million years ago.Why is that?Edited by randman, : No reason given.

You agree that 'if we evolved from apes, why are there still apes' is a silly argument, yes?What makes your argument that 'There are still, for example, non-vertebrates around." significantly different? Well, most of our debate comes down to this. We could just accuse each other of dodging arguments or we can try to understand each other, ask pertinent questions and try and move things forward. If
you feel the avenue is not fruitful we can simply stop.Here is my position again:Any children nodes of phyla will be called a subphyla, and then superclasses and then classes and so on. We wouldn't call the descendants of a superclass a new phyla.If a new phyla did crop up - it wouldn't be a nested hierarchy.You haven't explained why new phyla should have to crop up according to evolution or taxonomy. All you've said is that it has been a long time.If you feel that is avoiding your argument then there really isn't any advancing of the discussion to be made as far as I can see. Perhaps you can expand a little and a light bulb will go on and we can take a new direction.

Apes are not the discussion and I am frankly not interested in entertaining an argument based on apes and people on this thread. Actually, I have. If the mechanism for creating the phyla were in place still, new phyla would continue to be created or evolved and they are not.

So you agree it's a silly argument. Great. Now, how is your argument about how invertebrates exist not just the same argument, but moving back the focus a few orders of magnitude? There is no phyla-creating-mechanism. There is just evolution of life. There are some distant ancestral nodes, from which all extant animal life has descended from and we call this group of nodes 'phyla' for the purposes of classification.Edited by Modulous, : No reason given.

I don't agree it is a silly argument, and more to the point, I think you need to take a comprehensive look at what is being said.On apes or whatever for example, if evolution is a random process, there is no reason to think the theorized common ancestor of anything would evolve the same thing twice.Right?There is every reason, however, to think they would continue to evolve. So if new phyla evolved, you should expect that to keep happening and it has not.So if non-vertebrates evolved vertebrates hundreds of millions of years ago, why have they not evolved something else on the same magnitude (phyla)?Why don't we see some plan with the complex nerves and say, a horizontal backbone or whatever the imagination can come up with, assuming a random process? If not that, then at least several or many new lines of vertebrates?But the process seems to have stopped....why?Edited by randman, : No reason given.Edited by randman, : No reason given.

randman, Vertebrata isn't a phylum, it is a subclade of phylum chordata. You unwittingly make my point for me. Whatever evolves from chordate stock remains in the monophyletic group chordata. It matters not one iota whether it can fly, breathe underwater or just sits plant-like on a rock filter feeding. If its ancestors were chordates, it is a chordate. It cannot be in two phyla at once.If something within phylum chordata without a vertebral column evolves a vertebral column, it may warrant a new taxon all of its own, but that taxon will be within phylum chordata, not outside of it. No new phylum. As already pointed out, & if we suspend current classifications to allow vertebrata to be a phylum, anything that evolved from vertebrates would still belong to phylum vertebrata. It may be a new clade requiring a new name, but it will be a subclade of phylum vertebrata. You will never get a new phylum from a phylum.Mark

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There are 10 kinds of people in this world; those that understand binary, & those that don't

Randman - let me try to explain what Modulus is saying to you, as I don't think you have got it.Phylum is a taxonomic rank. (plural=phyla). Taxonomy deals with classification (at least traditionally) and only secondarily with evolution. Modern taxonomists try to classify according to evolutionary relationships, but the taxonomic system (which goes back to Linnaeus) is in many ways imperfect for this. Still, we need to be able to refer to particular groups of organisms using terms that are unambiguous and universally understood, so the system survives.The distribution in time of the origins of the various organismal groups corresponding to phyla has less to do with the frequency of major new body plans arising and far more with the problems in the imposition of a /ranked/ hierarchy on life, which is fundamentally a nested hierarchy without ranks. Think about the famous birds/reptiles example. Birds represented a significant new body plan arising from reptiles, and in traditional taxonomy are recognised as a class (as are reptiles). This means that reptiles are an artificial group, as the particular group of reptiles from which birds evolved share a more recent common ancestor with birds than they do with the rest of reptiles.It's the same with most of the phyla. They didn't all arise equally independently from each other, so for example vertebrates and echinoderms (starfish etc) share a common ancestor with each other more recently than either do with arthropods. So "phylum" doesn't really mean very much, and most people interested in evolutionary history these days don't really talk about phyla, they talk about echinoderms, vertebrates, the group that includes enchinoderms and vertebrates, the group that includes arthropods and velvet worms, and so on. In defining phlya, traditional taxonomists looked for the most inclusive groups, i.e. the ones that had other definable groups nested within them (classes, orders families etc), and because generating diversity takes time, these necessarily tend to be older clades. Simply, the requirement of the system to have ranks meant that the most inclusive ranks pretty much had to be old.I think the question you are trying to ask though is "why did all the major body plans arise in the Cambrian (or whenever) and not continuously throughout time?" - and as has already been pointed out, they didn't, they have popped up all the time but aren't called phyla, because the later they have arisen the more nested they are in the hierarchy. If something equivalent to a new phylum in the way you understand it popped up tomorrow (or a mere million years ago) it wouldn't be a new phylum, it would just be a highly unusual member of an existing phylum. If it so happens that in 500my time it has diversified into a major group with definable characteristics, its relationships to all other groups have become obscure through extinction and other processes, and there are still Linnaeun taxonomists around to think about it, then maybe it will become a new phylum..

exon, Spot on & well put.Mark

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There are 10 kinds of people in this world; those that understand binary, & those that don't

You think that 'if we evolved from apes, why are there still apes?' is not silly? OK, I thought we could at least agree on that but if not, we'll try to move on. Right. However, evolution isn't a random process. And the question I'm asking is - why should this be the case? If there is no reproductive advantage to be found in rejigging an established body plan then it won't get selected for. Think of it in terms of a fitness landscape - if a population is at the top of a hill, it is improbable that an animal could 'jump' onto another hill without taking a massive hit in reproductive fitness. The only realistic way it would happen is if there is a gradual uphill slope to another hill and there is no necessity for that to be the case. The process hasn't stopped - there's just no going back to the drawing board. We're stuck on the path our ancestors have tread upon. To get to the point where an animal would improve its fitness by evolving a spine, they may well have to go back down the fitness slope (decreasing their fitness) and start climbing up another one. This is completely against what evolution would predict as probable.Just because some primitive invertebrates were more successful with primitive notochords and the like it doesn't mean all would have been more successful and it doesn't mean that modern invertebrates would likewise find that this is the case. If competition is stiff to be the best in their niche - it might be that in order to get to a better solution they would first need to go through a period of taking a reduction in fitness. Clearly something that natural selection would not favour.This is more of a question of 'macroevolution' than it is about nested hierarchies. You must accept that evolution predicts nested hierarchies, surely? If we were sat in the lab and we witnessed a nematode evolve something which we could reasonably call a backbone it wouldn't jump from the nematode phylum to the chordata phylum and nor would a new phylum be created for them. They'd be in the nematode phylum. We'd just have to not say that all members of the nematode phylum are missing a backbone.Edited by Modulous, : No reason given.

I may be misunderstanding some of the replies, but isn't asking why no new phyla are forming today the same as asking why you're not gaining any new great great grandfathers?Though I've just participated, I'm reserving my right to moderate this thread. I'll try to keep my participation light.--Percy